Fractures of the proximal humerus can occur in patients of any age; however, these fractures have been found to occur more frequently in older patients, particularly elderly females who may suffer from osteoporosis. Such fractures usually occur in predictable fracture patterns and are commonly caused by falls where an arm was outstretched in an attempt to break the fall. Due to the compressive and varus forces about the shoulder, there is a tendency for the humeral head fragment to collapse in varus and settle distally.
Treatment of such fractures has, in past decades, tended to use a screw and fixation plate system where the fractured portion of the humeral head is first realigned, if displaced, and the proximal end of the humerus is then stabilized by multiple screws that attach a fixation plate to the surface of the humerus opposite from the surface where the fracture has occurred. Use of such plates for this purpose is well known and is shown, for example, in U.S. Pat. No. 7,604,657 and Published Application No. 2009/0326591. Such fixation or bone plates usually include a variety of holes, some of which are dedicated to elongated compression screws for passage through the head of the humerus into the fractured segment, whereas other holes are dedicated for the passage of a K-wire for alignment purposes, or for sutures for use in compressing the fractured bone part against the humerus, or for screws to securely mount the plate to the cortical bone of the humerus.
A wide variety of mechanisms have been developed for locking these elongated compression screws to the fixation plate so as to prevent incidental subsequent movement of the screws that might result in screw back-out, which has been felt to be undesirable toward retaining the fractured section of the humeral head in alignment. Some of these locking systems have used a variety of inserts for positioning within the cavities in the fixation plate where the heads of the elongated screws would reside, such as those shown in U.S. Pat. Nos. 5,578,034; 6,695,846; 7,004,944 and 7,273,481, designed to lock the heads. Alternative solutions have resulted in employment of a variety of plates or detents which are fastened in some manner so as to abut the heads of the elongated screws and thus positively block any back-out of the screw heads within the fixation plate; examples of such are shown in U.S. Pat. Nos. 4,794,918; 6,406,478; 6,413,259; 6,652,525 and 7,060,067, and in Published Patent Application 2006/0122605.
Over the years, it has been found that, during post-surgery, the fractured portion of the humeral head may frequently settle upon the closing of the fracture gap, and the amount of such settling can often be significant. The result has often been the protrusion of the pointed tips of the elongated compression screws through the cortical bone of the fractured portion, resulting in the emergence of these pointed tips in the articular surface of the humerus.
Effective locking plate systems particularly suited for the treatment of proximal humeral head fractures which avoid potential screw tip protrusion into the articular surface of the humeral head have accordingly been sought.